Higher concentration in serum of insulin autoantibodies in patients with schizophrenia or related psychosis, compared to in control subjects.

Objectives: In a recent study, we found increased antibody reactivity against the insulin receptor-A and insulin-like growth factor 1 receptor and their ligands in patients with schizophrenia or related psychosis, indicating that an autoimmune-mediated process may underlie development of schizophrenia. The aim of this study was to supplement our previous study with analysing additional neuronal- and diabetes-associated autoantibodies of potential interest for schizophrenia in the same patients and controls as in the foregoing study.

Material and methods: Analyses of neuronal (NMDAR, VGKC, AMPAR, GABABR, DPPX, GAD)- and voltage-gated calcium channel (VGCC) autoantibodies in cerebrospinal fluid (12 patients, 11 controls) and of diabetes-associated (GAD, IA-2, ZnT8, insulin)- and VGCC autoantibodies in serum (17 patients, 11 controls) were done by standard methods. Additionally, patients (n = 16) were accessed for clinical symptoms with the Positive and Negative Syndrome Scale (PANSS) for schizophrenia.

Results: Concentrations in cerebrospinal fluid of NMDAR-, VGKC-, AMPAR-, GABABR-, DPPX-, GAD- and VGCC autoantibodies were below detection limits in all patients and controls. Concentration in serum of insulin autoantibodies was significantly higher in patients than in controls (p = 0.001), whereas no significant differences were found in concentrations in serum of GAD-, IA-2-, ZnT8- or VGCC autoantibodies between patients and controls. Patients' serum concentrations of insulin autoantibodies tended to inversely correlate to their PANSS scores.

Conclusion: In this study, we show higher concentration in serum of insulin autoantibodies in patients with schizophrenia. This finding is of importance since autoantibodies against insulin may be implicated in the autoimmune-mediated process underlying development of schizophrenia.